Wet-spinning process



Patented June 5, 1951 WET-SPINNING PROCESS Joseph. Gordon: Galtom.Bu'fialo, andQaentin John OBrien Kenmore, N. Y., assignors. to E. I.. duPont de Nemours; & Company, Wilmington, Del.,.acorporationof Delaware NoDrawing. Application February 13; 1947.

Serial No. 728,372,

8 Claims. (01. 18- 54') This invention relates to, an improvedv processfor the formation of shaped. polymeric materials. In particular, thisinvention is concerned with an improved method for wet-spinningacrylonitrile; polymer and copolymers, thereof contain,- ing at least;85% acrylonitrile.

The processof this invention is generally applicable to the productionof any shaped article, as, for example, yarns, films,.b.r.istles. tubingand the. like. For convenience, the discussion herein is directedchiefly to. the production of yarns of polymers of acrylonitrile by thewet. spinning method.

It has been disclosed, for example, in U. Patent 2,40%,722 and incopending application W. W. Watkins, Serial No. 496,376, issued as. U.S. Patent. No. 2,426,119, that solutions: of acrylonitrile polymers orcopolymers can beextruded into coagulating baths, thereby forming yarns,films, etc., The apparatus described. therein or similar apparatus maybe used in this. invention. If solvents; of. fairly low boiling points,e. g.,.1-50 (3., are used,v hot. glycerol,.e.

120 15.0150. may be employed as, a coagulating bathto produce yarnhaving a dry tenacity of 2 to 4 grams per denier. However, it; isfrequently desirable: to use polymer solvents. having high boilingpoints. In this casev the. use of hot ycerol as a spinning. bathdoes notlead. to maximum yarn ten'acities because the yarn sets up very slowly.Under these conditions extreme care and a long. bath, travel arerequired to complete coagulation. Furthermore, special spinning rollersmust. be used in the bath to prevent. the development of high tensionsprior ta the wind-up because the yarn sets up so slowly. Thesedisadvantages slow the rate of production materially and the process isnot of commercial value. A spinning procedure which would permit the useof friction snubbing devices normally used in wet-spinning wouldconsiderably simplify the process and. allow the production of. highertenacity yarns. under optimum conditions.

This invention has as. an object. the improvement of yarn properties ofpolyacrylonitrile and.

its copolymers obtained by wet spinning fromhigh boiling solvents. Afurther object is the provision of coagulating baths which permit fastercoagulation of wet-spun. yarn. A still further object. is the provisionof spinninsmetm;

ads which permit the use of higher yarntake-up speeds. and increasedspinning: tensionsi yQther objects will appear hereinafter.

These obiects are accomplished by dissolving polyacrylonitrile. in a,suitable high boiling water-r soluble solvent extruding the solution,through a spinneret. into. a hot. glycerinecoagulating bath,.

and after a short. travel. passing the yarn from the glycerine baththrough a water dip. After the water treatment the yarn may be eithertaken up. immediately or passed through a second hot glycerine bathbefore collecting on a, spinning bobbin. After washing; and. drying. theyarn. is stretched andheat-treated in air. The inter mediate water bathin this case accelerates the setting up of the warm. Due. to the fasterrate of yarn coagulation, higher spinning tensions can be used andconsequentlyhigher tenacity yarn is formed.

The following examples in which parts... Dercentages, and proportionsare by weight are: given to illustratethe principles-of this inventionand. are not to be. considered as limitative.

v Etcamples Eleven parts of acrylonitrile. polymer, prepared by thepolymerization of monomeric. acrylonitrile in accordance with theteachingsof U. S. Patent. No. 1160;0541 to Bauer et al'.,.and possessingan average molecular weight of 89,000: as determined by the Staudingerequation from viscosity data, are ground to an average particle size. ofv mesh and mixed with 89.. parts of tetramethylene sulfone to form athin slurry. Air entrapped in the polymer slurry is removed using vacuumtechniques: The'slurryis then heated to C. over a' period of 30 minutesto form a clear soluti'on possessinga viscosity of 1'80 p'oises at C.This solution is" extruded through a (SO-hole spinneret'into a glycerolprecipitating bath (a) heated to a temperature of 140 C; The delivery ofthe spinneret is-6 gramsper minute. The yarn formed thereby travelsthrough this bath as described in the table below. During thecoagulating period theyarn is given a room temperature water dip- ('b).This treatment is omitted in the control experiment below. A secondglycerol bath (0) may be used. The spinning tension is as descr-ibedinthe followingtable. The yarn is 'collectedon a bobbin wind-up andpressure washed with water. on the bobbin. The

Optimum Dry Spinning Bath Spinning mer'stretch Drawn Yarn C(Trave nd)Tension, Denier omposi 1011 grams T m W E1ng O ity ation Control. go;78: glyoerine-.. 6X 162 74.4 4. 62 6.0 1 fg f 30 "x 174 56.7 5.10 1.2

(a 27' gIyceIineIZ 2 4' water; 73 1. 75X 183 99. 6 6. 23 7.4

c) 3' glycerine- 1 Too low to measure accurately.

when only a glycerine bath is used, 78" of bath travel are required, thespinning tensions being too low to measure accurately and specialspinning rollers are required. However, when a water bath is used inconjunction with the glycerine coagulating bath, only 31 to 34" of bathtravel are needed and the normally used snubbing devices can beemployed. The fact that the optimum after-stretch ratios in Examples 1and 2 above are considerably lower than that in the control exampleindicate that in the processes of this invention some of the stretchingoccurs in the spinning baths whereas little or no stretching does or canoccur in the control. Further, the use of the two component bath systemleads to yarns having substantially improved tenacities and elongations.The faster rate of coagulation under tension leads to partialorientation and a yarn with a 10 to 35% higher tenacity plus anincreased elongation.

A suitable solvent within the scope of this invention is one with arather high boiling point i. e., above 200 C. In the case of a solventof fairly low boiling point (e. g., dimethylformamide), the glycerolbath at the temperatures employed acts to set up the yarn at aconveniently fast rate and no water dip is required for attainment ofhigh yarn porperties. However, when solvents having a high boilin point,say above 200 C., are employed, the glycerol temperatures used do notremove solvents from the coagulating filament at a desirable rate. Thisoccurs probably, because the low vapor pressure of the solvent at thespinning temperatures causes relatively little solvent to be removed byevaporative processes and only solution processes arising from thesolubility of the solvent in the bath are operative. In the process ofthis invention the use of a water dip results in a considerable increasein rate of coagulation with consequent improvement in the physicalproperties of the yarn.

While tetramethylene sulfone is described herein as a suitable solventfor the wet spinning of polyacrylonitrile by this invention, it is to beunderstood that the method may be applied to spinnin from other solventsas well. As examples of suitable polyacrylonitrile solvents which areuseful in the process of this invention are the water-soluble solventsdisclosed in U. S. Patents Nos. 2,404,714-2,404,727, inclusive, whichpossess high boiling points, for example, in excess of 200 C. Thus, ingeneral, this invention is applicable broadly to the use of any highboiling water-soluble organic solvents for the acrylonitrile polymers.Specific solvents which may be mentioned here for; illustrative purposesinclude malononitrile, methyl ethyl sulfoxide and methyl ethyl sulfone.

The temperature of the water dip may be varied from 0 to 100 C. Roomtemperature, however, is most convenient and. gives excellent results.

The glycerine bath temperatures may be from 100 C. to 160 C., but atemperature of about 140 C. gives optimum yarn properties. The length oftravel of the yarn through the glycerine and water baths depends uponthe rate of coagulation of the yarn. The bath length will also varydirectly with the spinning speed. Since the water dip accelerates therate of yarn coagulation, the length of travel through the glycerinebath can be much less than when used without a water dip. The use of thewater dip as described herein accelerates the rate of coagulation of aspinning solution from 10 to 75% or more.

While for purposes of convenience this :process is described withrelation to a glycerine coagulating bath, it is to be understood thatthe other non-aqueous coagulating mediums may be used as well. It isonly necessary that the bath be capable of precipitating the polymersfrom its solutions. As examples of other baths that are operative in anyof the processes of this invention may be mentioned triethanolamine andhexaethylene glycol. Thus, when a plurality of nonaqueous baths is used,the baths may be alike or different. The main determining factor is thatthe baths used must be capable of coagulating or further coagulating thespinnin solutions in a short period of time to facilitate rapid spinningof yarn.

The spinning tensions are applied by means of the usual frictionsnubbing devices described elsewhere in the wet-spinning art. Yarns spunfrom high boiling solvents without an intermediate water dip cannot besubjected to the desired spinning tension, because of the slow rate ofcoagulation. Since yarns spun under low tension do not develop optimumproperties, it is especially advantageous to be able to subject the yarnto tension as it coagulates.

The after-stretch ratio for wet-spun acrylonitrile polymer usually issomewhat lower than that experienced with dry spun yarn. Generally, thisratio may be from 1.5X to 9X with the range of 1.'75X to 5X preferred.

The temperature of the after-stretching largely depends on the physicaland chemical properties of the polymer. For yarns prepared from thepreferred range of polymers of acrylonitrile within the scope of thisinvention, after-stretch ing temperatures of C. to 210 C. are possiblewith the range C. to 0. preferred. The yarn after-stretching may becarried out on any suitable apparatus which allows the yarn to be heatedprior to drawing. A preferred process and apparatus is described in thecopending application of Daniel T. 'Meloon, Serial Number guesses496,397, filed July 28; 1943, nowabandonded. Another process might bethedrawing ofthe yarn as it passes through a heated medium, such;

as a hot vapor or liquid. When they stretching operation is carried outin the presence of steam or other vapor, the preferred temperaturerange: is considerably lower, 1. e., 110 C. to 140 C.

A greater degree of elongation in. the finished yarn may be obtained byallowing the yarn to relax (5-15%) immediately after drawingmay beaccomplished by passing the yarn over a hot plate or through a heatedatmosphere at a temperature slightly above the draw temperature andallowing the yarn to relax (contract) the desired amount by running thetake-up roll the desired relaxed ratio percentage slower than the feedroll.

The heat-treating of polyacrylonitrile yarn to improve elongationwithout loss in tenacity may be carried out by heating the yarn cones ina thermostatically controlled oven or other suitable means. The time ofheat treatment will normally vary inversely with the temperature.Depending upon the heat-treating temperature, the time may be variedfrom 1 to 10 hours at temperatures of 100 C. to 200 C. When heattreatingthe yarn, care must be taken to avoid subjecting it to such a severetreatment that discoloration of the yarn results. The preferred range oftemperature is 100 C. to 150 C, for a treatment time of /2 to 2 hours.

The polymers for use in this invention preferably have molecular weightswithin the range of 15,000 to 250,000 or even higher as calculated fromviscosity measurements by the Staudinger equation:

Molecular weight= viscosity of solution N31): specific viscosity:

and

C=concentration of the solution expressed as the number of moles of themonomer (calculated) per liter of solution.

Polyacrylonitrile itself may be used and copolymers of acrylonitrilewith such monomers as vinyl esters, vinyl halides, vinylidene halides orother ethylenic compounds such as ethylene or butadienes may be employedin the process of this invention.

The use of a water dip in the wet-spinning process of this inventionallows the production of higher tenacity yarn. When the yarn has passedaround friction snubbing devices in.the water dip or immediatelythereafter, it tends to become partially oriented while in the gel orpartially swollen state. This allows the formation of a stronger, betteryarn. If a water dip is not used, it is very difficult to apply highspinning tension to the yarn. In addition, the slow rate of coagulationnecessitates a very long bath travel and slow wind-up speed.

Furthermore, the vrocess of this invention allows the use of highboiling solvents that would otherwise have little commercial value dueto the excessive length of time necessary to set up the yarn as it isspun. In the process of this invention, high boiling solvents can beused at temperatures considerably below their boiling point, thus makingcommercially available a large num- 6. her of suitable solvents for thespinning of polyacrylonitrile yarns.

Any departure from the above description Which conforms to the presentinvention is intended to be included within the scope of the claims.

We claim:

1. A process for wet spinning'of yarn of an acrylonitrile polymercontaining at least of acrylonitrile which comprises extruding asolution of said polymer in a high-boiling, watersoluble organic solventthrough a shaped orifice into a first coagulant spinning bath selectedfrom the group consisting of glycerol, triethanolamine and hexaethyleneglycol, thereby precipitating said polymer from its said solution in theform of yarn; passing said yarn into a second coagulant bath consistingof water; and subsequently into a third coagulant bath selected from thegroup consisting of glycerol, triethanolamine and hexaethylene glycol,and stretching said yarn during the spinning.

2. A process according to claim 1 in which the said first and thirdcoagulant baths consist of glycerol.

3. A process according to claim 1 in which the said first and thirdcoagulant baths consist of triethanolamine.

4. A process according to claim 1 in which the said first and thirdcoagulant baths consist of hexaethylene glycol.

5. A process in accordance with claim 1 in which the said water bath isheated to a temperature of from 20 to C. and the said first and thirdbaths are heated to a temperature of about 100 C.

6. A process for wet spinning of yarn of an acrylonitrile polymercontaining at least 85% of acrylonitrile which comprises extruding asolution of said polymer, in a high-boiling, watersoluble organicsolvent, through a shaped orifice into a spinning, coagulant bathconsisting of glycerol heated to a temperature of at least 100 C.;passing the yarn formed thereby into a second coagulant bath consistingof water heated to a temperature from about 20 C. to about 100 0.; andpassing said yarn into a third coagulant bath consisting of glycerolheated to a temperature of at least 100 C.; and stretching said yarnsduring the spinning.

'7. A process for Wet spinning of yarn of an acrylonitrile polymercontaining at least 85% of acrylonitrile which comprises extruding asolution of said polymer in tetramethylene cyclic sulfone through ashaped orifice into a first coagulant spinning bath selected from thegroup consisting of glycerol, triethanolamine and hexaethylene glycol,thereby precipitating said polymer in the form of yarn from a solutioncomprising about 89% tetramethylene cyclic sulfone and about 11% saidpolymer; passing the yarn formed thereby into a second coagulant bathconsisting of water; passing said yarn from said second bath into athird coagulant bath consisting of glycerol; and stretching said yarnduring the spinning.

8. A process for wet spinning of yarn of an acrylonitrile polymercontaining at least 85% of acrylonitrile which comprises extruding asolution of said polymer in a high boiling water soluble organic solventthrough a shaped orifice into a glycerol coagulant spinnin bath heatedto a temperature of about 100 (3., thereby precipitating said polymerfrom its said solution in the form of yarn; passing the said yarnthrough the said glycerol coagulant spinning bath for a distance'ofabout 2'7 inches; passing 'said-- yarn through a second coagulatingbath'consisting of 7 REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PA'I'ENTS Number Name Date Rochet Mar. 20, 1934 Houtz Nov.6, 1945 Latham July 23, 1946 Houtz July 23, 1946 Watkins Sept. 2, 1947

1. A PROCESS FOR WET SPINNING OF YARN OF AN ACRYLONITRILE POLYMERCONTAINING AT LEAST 85% OF ACRYLONITRILE WHICH COMPRISES EXTRUDING ASOLUTION OF SAID POLYMER IN A HIGH-BOILING WATERSOLUBLE ORGANIC SOLVENTTHROUGH A SHAPED ORIFICE INTO A FIRST COAGULANT SPINNING BATH SELECTEDFROM THE GROUP CONSISTING OF GLYCEROL, TRIETHANOLAMINE AND HEXAETHYLENEGLYCOL, THEREBY PRECIPITATING SAID POLYMER FROM ITS SAID SOLUTION IN THEFORM OF YARN; PASSING SAID YARN INTO A SECOND COAGULANT BATH CONSISTINGOF WATER; AND SUBSEQUENTLY INTO A THIRD COAGULANT BATH SELECTED FROM THEGROUP CONSISTING OF GLYCEROL, TRIETHANOLAMINE AND HEXAETHYLENE GLYCOL,AND STRETCHING SAID YARN DURING THE SPINNING.